Investigations into the preparation of groups 13-15 N-heterocyclic carbene analogues

Article abstract of DOI:10.1016/j.ica.2006.12.014

Attempts have been made to prepare a variety of groups 13-15 N-heterocyclic carbenoid systems. The work in group 13 led to two structurally characterized, paramagnetic gallium(III) heterocycles, [I₂Ga{[N(R)C(Me)]₂}], R = C₆ H₃ Pr₂ⁱ - 2, 6 (Ar) or C₆H₃(C₆H₄Bu^t-4)₂-2,6. Reduction of the former gave the anionic gallium(I) heterocyclic complex, [K(tmeda)][:Ga{[N(Ar)C(Me)]₂}], which was oxidatively coupled, affording the structurally characterized digallane(4), [Ga{[N(Ar)C(Me)]₂}]₂. From group 14, the new germanium(IV) heterocycle, [Cl₂Ge{[N(Ar)C(H)]₂}], and the N-heterocyclic germylene, [:Ge{[N(Ar)C(H)]₂}], have been prepared and fully characterized. Attempts to prepare N-heterocyclic silylene, phosphenium and arsenium compounds were unsuccessful and led instead to the silyl, phosphino and arsino-substituted ene-amines, [(Cl_nE)₂{μ-[N(Ar)C(H)]₂}], E = Si, n = 3; E = P or As, n = 2.

Full text of DOI:10.1016/j.ica.2006.12.014

Available online at www.sciencedirect.com
Inorganica Chimica Acta 361 (2008) 427–435
www.elsevier.com/locate/ica
Investigations into the preparation of groups 13–15 N-heterocyclic
carbene analogues
a
a,b,
a
a
Robert J. Baker , Cameron Jones
*, David P. Mills a,b, Glesni A. Pierce , Mark Waugh
a
Centre for Fundamental and Applied Main Group Chemistry, School of Chemistry, Main Building, Cardiff University, Cardiff CF10 3AT, UK
b
School of Chemistry, Monash University, P.O. Box 23, Vic., 3800, Australia
Received 31 October 2006; received in revised form 4 December 2006; accepted 5 December 2006
Available online 15 December 2006
Dedicated to Professor Tony Downs on the occasion of his 70th birthday.
Abstract
Attempts have been made to prepare a variety of groups 13–15 N-heterocyclic carbenoid systems. The work in group 13 led to two
structurally characterized, paramagnetic gallium(III) heterocycles, [I2Ga{[N(R)C(Me)]2}], R ¼ C6H3Pri -2; 6 ðArÞ or C6H3(C6H4But-4)2-
2
2,6. Reduction of the former gave the anionic gallium(I) heterocyclic complex, [K(tmeda)][:Ga{[N(Ar)C(Me)]2}], which was oxidatively
coupled, affording the structurally characterized digallane(4), [Ga{[N(Ar)C(Me)]2}]2. From group 14, the new germanium(IV) heterocy-
cle, [Cl2Ge{[N(Ar)C(H)]2}], and the N-heterocyclic germylene, [:Ge{[N(Ar)C(H)]2}], have been prepared and fully characterized.
Attempts to prepare N-heterocyclic silylene, phosphenium and arsenium compounds were unsuccessful and led instead to the silyl, phos-
phino and arsino-substituted ene-amines, [(ClnE)2{l-[N(Ar)C(H)]2}], E = Si, n = 3; E = P or As, n = 2.
Ó 2006 Elsevier B.V. All rights reserved.
Keywords: Gallium; Germanium; N-heterocyclic carbenoid; Low oxidation state; Crystal structure
1. Introduction
Five-membered NHC analogues are now known for all
the second to third row elements of groups 13–16, except
Al, In, S and Te (Chart 1) [1–7]. It should also be noted
that a boron NHC analogue (E = B, R ¼ C6H3Pri2-2; 6
ðArÞ, charge = ꢀ1), which represents the first structurally
characterized boryl anion, has recently been reported
[11]. All of these heterocycles possess a lone pair of elec-
trons at the carbenoid center and thus could potentially
act as Lewis bases in the formation of metal complexes.
Indeed, structurally characterized complexes are known
for examples of all the heterocycles except those where
E = Sb or Se. This is not surprising as these would be the
most electrophilic of the series.
The study of low oxidation state p-block compounds is
one of the most widely investigated areas of modern main
group chemistry. Within this field valence isoelectronic
analogues of five-membered N-heterocyclic carbenes
(NHCs) have proved particularly attractive targets to syn-
thetic chemists (Chart 1) [1–8]. The reasons for this must
include fundamental interest in such systems, but also their
potential to act as ligands in the formation of novel com-
plex types. This potential is now well demonstrated
[2,8,9], and like NHCs [10], the complexes of these hetero-
cycles are beginning to find synthetic applications [2,8].
To date, our interest in the field has lain with an anionic
gallium(I) heterocycle (E = Ga, R = Ar, 1) which we have
employed as a ligand in the formation of a wide variety of
s-, p- and d-block metal complexes [8,12]. This work has
demonstrated a close analogy between the coordination
chemistry of this heterocycle and that of NHCs in that it
*
Corresponding author. Address: Centre for Fundamental and Applied
Main Group Chemistry, School of Chemistry, Main Building, Cardiff
University, Cardiff CF10 3AT, UK. Tel.: +44 29 20 874 060; fax: +44 29
20 874 030.
E-mail address: jonesca6@cardiff.ac.uk (C. Jones).
0020-1693/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2006.12.014

428
R.J. Baker et al. / Inorganica Chimica Acta 361 (2008) 427–435
portion reactions, gave the paramagnetic gallium(III) com-
plexes, 2 and 3, in moderate yields (Scheme 1). It is of note
that the terphenyl substituted DAB ligand has previously
been used to prepare chiral C2-symmetric transition metal
complexes [13]. The reduction of 2 with an excess of potas-
sium metal in THF led to the new anionic gallium(I) het-
erocyclic complex, 4, in good yield. Unfortunately, a
similar reduction of 3 led only to an intractable mixture
of products for unknown reasons. It is worthy of note that
the reduction of 2 with calcium metal has previously been
reported to give the first calcium-gallyl complex, [Ca{Ga
[N(Ar)C(Me)]2}2(THF)4] [14].
We have previously shown that 1 can be readily oxida-
tively coupled in its reaction with the ferrocenium cation
to give a digallane(4), [Ga{[N(Ar)C(H)]2}]2 [12g,15]. This
compound was subsequently used as a precursor to transi-
tion metal–gallyl complexes via oxidative addition of its
Ga–Ga bond to low valent metal centers [12b]. Considering
this, and the scarcity of related digallane(4) compounds,
the oxidative coupling of the anionic heterocycle of 4 by
its treatment with Tl2SO4 was carried out and led to the
new digallane, 5, in moderate yield (NB: Treatment of 4
with the ferrocenium ion also gives 5). This route is favor-
able to that employing the ferrocenium cation as both by-
products, thallium metal and K2SO4, are insoluble in THF
and are easily filtered off from the reaction mixture.
As 2 and 3 are paramagnetic, no meaningful NMR data
could be obtained for these complexes. They were, how-
ever, examined by solution state EPR spectroscopy at
120 K and 300 K, but all resultant spectra revealed broad,
unresolved signals, as has been seen before for similar com-
plexes [1a,16]. The g-values determined for both complexes
(2 2.0025, 3 2.0015) are close to free spin (g = 2.0023),
charge
R
charge
E =
-1
0
+1
P
As
Sb
+2
Se
E
Si
Ge
Sn
R
N
N
Ga
Chart 1.
can, for example, stabilize low oxidation state and/or ther-
mally labile metal fragments. As a result of our success in
this area, we wished to extend the catalogue of anionic gal-
lium(I) heterocycles. In addition, we hoped to prepare a
variety of group 14 and 15 heterocycles incorporating Ar
and other substituents in order that we could make direct
comparisons between coordination chemistry of these and
that of our gallium(I) heterocycle, 1. Our efforts in this
direction are reported herein.
2. Results and discussion
2.1. Group 13 chemistry
Sterically bulky N-substituents are essential for the sta-
bilization of anionic group 13 metal(I) heterocycles such as
1. Extra steric bulk could be incorporated into these het-
erocycles by adding substituents to the backbone carbon
atoms. It was, therefore, our intention to prepare backbone
substituted gallium(I) heterocycles with the bulky N-sub-
stituents, Ar or the terphenyl C6H3(C6H4But-4)2-2,6. A
similar synthetic route to that used in the preparation of
1 was chosen. That is, the appropriate diazabutadiene
(DAB) was reacted with ‘‘GaI’’ which led to a 1-electron
reduction of the DAB ligand, which in concert with dispro-
N
R
''GaI'', toluene
- Ga(s)
R
N
I
N
I
R
Ga
R
N
R = C6H3Pri2-2,6 (Ar) 2
or C6H3(C6H4But-4)2-2,6 3
i) K, THF
ii) tmeda
Ar
N
Ar
N
Ar
N
Tl2SO4, THF
[K(tmeda)]
Ga
Ga Ga
- Tl(s)
N
N
N
Ar
Ar
Ar
4
5
Scheme 1.

R.J. Baker et al. / Inorganica Chimica Acta 361 (2008) 427–435
429
which indicates the essentially organic nature of both rad-
icals. As the NMR spectra of 4 and 5 are consistent with
their solid state structures and are similar to those of the
equivalent potassium salt of 1 [1a] and the digallane(4),
[Ga{[N(Ar)C(H)]2}]2 [15], respectively, no comment will
be made here.
The X-ray crystal structures of 2, 3 and 5 were obtained
and are depicted in Figs. 1–3, respectively (see Table 1).
That for 2 is effectively isostructural with its backbone H-
substituted counterpart, [I2Ga{[N(Ar)C(H)]2}] [16], and
as in that compound the bond lengths within the N2C2
fragment are suggestive of significant delocalization. The
structure of 3 shows it to have a similarly delocalized
DAB ligand with Ga–I and Ga–N bond lengths close to
those in 2. The complex is, however, chiral (existing as both
enantiomers in the crystal) in that it has a C2 symmetric
coordination geometry due to the repulsive interactions
between the sterically demanding terphenyl substituents.
A similar situation exists for the PdCl2 complex of this
DAB ligand [13]. The structure of 5 is very similar to that
of [Ga{[N(Ar)C(H)]2}]2 [15], and as in that compound the
C2
2’
I1’
C
C1’
C1
C3’
N1
1’
N
3
C
Ga1
I1
Fig. 2. Molecular structure of 3 (hydrogen atoms omitted for clarity).
˚
Selected bond lengths (A) and angles (°): I(1)–Ga(1) 2.5205(6), Ga(1)–N(1)
1.939(3), N(1)–C(1) 1.341(5), N(1)–C(3) 1.437(4), C(1)–C(1)0 1.422(7),
N(1)0–Ga(1)–N(1) 84.79(18), N(1)–Ga(1)–I(1)0 122.12(9), N(1)–Ga(1)–I(1)
C3’
C2’
0
108.61(9), I(1)0–Ga(1)–I(1) 109.66(3). Symmetry operation: ꢀx + 1, y,
ꢀz + 3/2.
N1’
C1’
bond lengths within the DAB fragment are indicative of
localized C–C double and N–C single bonds, cf. the DAB
delocalization in 2. As the Ga–N bonds in 5 are covalent,
they are significantly shorter than the formally dative
Ga–N bonds in 2, despite the higher oxidation state metal
center in the latter. The Ga–Ga distance is in the normal
range1 and close to that in [Ga{[N(Ar)C(H)]2}]2
I
1
Ga1
I2
C1
N1
C2
˚
(2.3482(2) A) [15], whilst the two heterocycle least squares
planes bisect each other with an angle of 43.4°.
C3
2.2. Group 14 chemistry
The coordination chemistry of N-heterocyclic silylenes
(the Si analogues of NHCs) is now well developed [2]. In
contrast, only few complexes of N-heterocyclic germylenes
[3c] and stannylenes [4b] exist. We wished to explore the
coordination chemistry of Si and Ge heterocycles with an
ArNC(H)C(H)NAr (Ar-DAB) backbone, in order to
Fig. 1. Molecular structure of 2 (hydrogen atoms omitted for clarity).
˚
Selected bond lengths (A) and angles (°): I(1)–Ga(1) 2.5343(8), I(2)–Ga(1)
2.4949(8), Ga(1)–N(1) 1.929(3), N(1)–C(1) 1.353(4), C(1)–C(1)0 1.410(7),
N(1)0–Ga(1)–N(1) 85.72(17), N(1)–Ga(1)–I(2) 117.05(9), N(1)–Ga(1)–I(1)
1
0
113.04(9), I(2)–Ga(1)–I(1) 109.37(2). Symmetry operation:
3/2, z.
x, ꢀy +
As determined from a survey of the Cambridge Crystallographic
Database (October, 2006).

430
R.J. Baker et al. / Inorganica Chimica Acta 361 (2008) 427–435
SiCl3
N
Ar
Ar
N
6
i) Li, THF
ii) SiCl4
SiCl3
C4
C2
N2
N4
Ar
C32
C1
Ga2
N
C3
N
Ar
C30
C29
Cl
GeCl2.dioxane
toluene
Ga1
Ge
N1
Cl
N
Ar
N
Ar
7
N3
C31
Ar
N
i) Li, THF
ii) GeCl2.dioxane
Ge
N
8
Ar
Scheme 2.
Fig. 3. Molecular structure of 5 (hydrogen atoms omitted for clarity).
˚
Selected bond lengths (A) and angles (°): Ga(1)–N(1) 1.847(4), Ga(1)–N(2)
1.854(4), Ga(1)–Ga(2) 2.3634(9), Ga(2)–N(3) 1.842(5), Ga(2)–N(4)
1.847(5), N(1)–C(1) 1.404(7), N(2)–C(2) 1.408(7), N(3)–C(29) 1.420(8),
N(4)–C(30) 1.403(8), N(1)–Ga(1)–N(2) 88.3(2), N(1)–Ga(1)–Ga(2)
136.94(14), N(2)–Ga(1)–Ga(2) 134.70(14), N(3)–Ga(2)–N(4) 88.5(2),
N(3)–Ga(2)–Ga(1) 135.09(15), N(4)–Ga(2)–Ga(1) 136.40(15).
of a Lewis base. As [Cl2Si(DAB)] precursors to N-heterocy-
clic silylenes have been previously prepared by reaction of
Li2[DAB] with SiCl4 [2], we investigated the specific 1:1
treatment of Li2[Ar-DAB] with SiCl4 (Scheme 2). Instead
of the expected product, [Cl2Si(Ar-DAB)], the N-silylated
ene-diamine (6), was formed in low yield as the only iso-
lated product. Even when the reaction was repeated with
an excess of Li2[Ar-DAB] and the order of addition was
reversed, this was the outcome. It is not known why this
occurs but an intentional, high yielding preparation of 6
was devised whereby two equivalents of SiCl4 were treated
with Li2[Ar-DAB] in THF.
compare their coordination chemistry with that of 1 which
also contains the Ar-DAB backbone. There have been
recent reports on both heterocycles [17,18], though no syn-
thetic or spectroscopic details were given for the germa-
nium heterocycle, [:Ge(Ar-DAB)]. The silicon heterocycle,
[:Si(Ar-DAB)], was prepared by the potassium reduction
of [Cl2Si(Ar-DAB)], which itself was unusually prepared
by the reaction of Ar-DAB with HSiCl3 in the presence
Given that the reaction of Ar-DAB with ‘‘GaI’’ leads to
a reduction of the DAB ligand and formation of paramag-
Table 1
Crystal data for compounds 2, 3 Æ (diethyl ether)0.50, 5 Æ (diethyl ether)0.33, 7, 9 and 10
2
3 Æ (diethyl ether)0.50 5 Æ (diethyl ether)0.33
7
9
10
Chemical formula
Formula weight
T (K)
C
28H40GaI2N2 C58H69GaI2N2O0.5 C57.33H83.33Ga2N4O0.33 C26H36Cl2GeN2 C26H36Cl4N2P2 C26H36As2Cl4N2
728.14
150(2)
orthorhombic
Pnma
1125.67
150(2)
monoclinic
P21/c
973.39
150(2)
trigonal
520.06
150(2)
orthorhombic
Pnma
580.31
150(2)
triclinic
668.21
150(2)
triclinic
Crystal system
Space group
ꢀ
ꢀ
ꢀ
P3
P1
P1
˚
a (A)
13.370(3)
21.132(4)
10.558(2)
90
90
90
2983.0(10)
4
3.010
18.109(4)
10.864(2)
16.380(3)
90
116.00(3)
90
27.940(4)
27.940(4)
13.340(3)
90
90
120
12.037(2)
21.393(4)
10.467(2)
90
90
90
9.817(2)
10.577(2)
15.888(3)
73.82(3)
80.02(3)
75.09(3)
1521.8(5)
2
9.2640(19)
10.064(2)
16.466(3)
92.77(3)
97.47(3)
99.10(3)
1499.3(5)
2
˚
b (A)
˚
c (A)
a (°)
b (°)
c (°)
3
˚
V (A )
2896.3(10)
2
9019(3)
6
2695.3(9)
4
Z
l (Mo Ka) (mmꢀ1
)
1.576
0.931
1.350
0.512
2.603
Reflections collected (Rint
Unique reflections
R1 (I > 2r(I))
)
20684 (0.0907) 15870 (0.0691)
23338 (0.0812)
10171
0.0786
0.1963
22547 (0.0708)
3166
0.0344
0.0808
21803 (0.0651)
5928
0.0417
26 081 (0.0766)
6790
0.0573
3516
5878
0.0394
0.0889
0.0461
0.1202
wR02 (all data)
0.1003
0.1385

R.J. Baker et al. / Inorganica Chimica Acta 361 (2008) 427–435
431
netic [I2Ga(Ar-DAB)] [16], we speculated that treatment of
Ar-DAB with GeCl2 Æ dioxane might lead to a two electron
reduction and the formation of diamagnetic, [Cl2Ge(Ar-
DAB)]. This proved to be the case and led to the formation
of 7 in good yield (Scheme 2). It is worthy of mention that
the same methodology has recently been applied to the syn-
thesis of [Cl2Ge(But-DAB)] (But-DAB = {ButNCH}2) [3a].
Attempts were made to reduce 7 with potassium in THF
but these led to intractable mixtures of products in each
case. As the N-heterocyclic stannylene, [:Sn(Ar-DAB)],
has been prepared by reaction of Li2[Ar-DAB] with
SnCl2 Æ dioxane [4b], we carried out the equivalent 1:1 reac-
tion with GeCl2 Æ dioxane which gave 8 in good yield. The
coordination chemistry of 8 is being examined in another
study in our laboratory.
The spectroscopic data for 6 and 7 are unremarkable
and are consistent with their proposed structures so will
not be commented on here. Similarly, the data for 8 will
not be discussed, though they have not been previously
reported and, thus, are included in Section 4. An X-ray
crystallographic analysis of 7 was carried out and its molec-
ular structure is depicted in Fig. 4. The crystal structures of
6 and 8 were obtained but are not of publishable quality
due to very weak data in the case of 6, and extensive disor-
der of the heterocycle within the lattice in the case of 8.
Despite this, it is clear from the structures that the molec-
ular connectivity of the complexes is as proposed. Com-
pound
7 is monomeric and possesses a distorted
tetrahedral germanium center with bond lengths to the N
and Cl centers that lie in the normal range.1 The geometry
of the Ar-DAB backbone is indicative of it being localized,
as is the case in closely related complexes, e.g. [Cl2Ge(But-
DAB)] [3a].
2.3. Group 15 chemistry
Several cationic phosphenium and arsenium heterocycles,
[E(DAB)]+, E = P or As, have been reported [5] though none
incorporating the Ar-DAB ligand are known. A common
synthetic route to these systems involves the reaction of
Li2[DAB] with one equivalent of ECl3 which gives [ClE
(DAB)] which can either auto-ionize to give [E(DAB)][Cl]
[5d] or can be treated with chloride abstraction agents afford-
ing salts containing [E(DAB)]+ cations [5b]. The chlorodi-
azaphospholene, [ClP(Ar-DAB)], has previously been
prepared in the reaction of ArN@C(H)C(H)2N(H)Ar with
PCl3 and NEt3, but was not structurally characterized [5b].
We attempted to prepare this heterocycle by treating
Li2[Ar-DAB] with one equivalent of PCl3, but this reaction
yielded the diphosphinoeneamine (9), in low yield as the only
isolated product. Similarly, treating Li2[Ar-DAB] with one
equivalent of AsCl3 led to the arsenic analogue of 9, viz. 10
(Scheme 3). Similar to the reaction that gave 6, when these
reactions were repeated using an excess of Li2[Ar-DAB], 9
and 10 were the only isolated products. It is unknown why
these compounds form under the reaction conditions
employed, but higher yields of the complexes were obtained
when a 1:2 stoichiometry was used. The reduction of either 9
or 10 with an excess of potassium metal in THF led only to
insoluble materials and K2[Ar-DAB].
C1’
N1’
Cl2
Ge1
C1
The 1H and 13C{1H} NMR spectra of 9 and 10 are sim-
ilar and reflect their solid state structures. Compound 9
exhibits a singlet at d 141.7 ppm in its 31P{1H} NMR spec-
trum which, interestingly, is at almost identical field to that
reported for the heterocycle, [ClP(Ar-DAB)] (d 141.0 ppm)
[5b]. As 9 and 10 are effectively isostructural, only the
molecular structure of the former is included here, though
relevant metrical parameters for the latter are included in
the caption of Fig. 5. In both, the ene-diamide ligand
adopts a trans-stereochemistry and bridges two terminal
Cl1
N1
C2
ECl2
N
Ar
N
Ar
i) Li, THF
ii) ECl3
Fig. 4. Molecular structure of 7 (hydrogen atoms omitted for clarity).
˚
Selected bond lengths (A) and angles (°): Ge(1)–N(1) 1.8061(16), Ge(1)–
Ar
N
Ar
N
Cl(1) 2.1306(10), Ge(1)–Cl(2) 2.1434(9), N(1)–C(1) 1.412(3), C(1)–C(1)0
1.332(4), N(1)0–Ge(1)–N(1) 91.63(10), N(1)–Ge(1)–Cl(1) 117.32(6), N(1)–
Ge(1)–Cl(2) 114.80(5), Cl(1)–Ge(1)–Cl(2) 101.82(4). Symmetry operation:
E = P
9
E = As 10
ECl2
0
x, ꢀy + 3/2, z.
Scheme 3.

432
R.J. Baker et al. / Inorganica Chimica Acta 361 (2008) 427–435
1
Na/K then freeze/thaw degassed prior to use. H, 13C{1H}
and 31P{1H} NMR spectra were recorded on either a Bru-
ker DXP400 or Jeol Eclipse 300 spectrometer, and were
Cl2’
Cl1’
1
P1’
referenced to the residual H or 13C resonances of the sol-
vent used, or external 85% H3PO4, d 0.0 ppm (31P{1H}
NMR). Mass spectra were obtained from the EPSRC
National Mass Spectrometry Service at Swansea Univer-
sity. IR spectra were recorded using a Nicolet 510 FT-IR
spectrometer as Nujol mulls between NaCl plates. Microa-
nalyses were obtained from Medac Ltd. Melting points
were determined in sealed glass capillaries under argon,
and are uncorrected. {N(R)C(Me)}2, R = Me [19] or
C6H3(C6H4But-4)2-2,6 [13]; {N(Ar)C(H)}2 [20] and ‘‘GaI’’
[21] were synthesized by literature methods. All other
chemicals were obtained commercially and used as
received.
N1’
C1’
C2
C1
N1
Cl1
P1
Cl2
Fig. 5. Molecular structure of 9 (hydrogen atoms omitted for clarity).
4.1. [I2Ga{[N(Ar)C(Me)]2}] (2)
˚
Selected bond lengths (A) and angles (°): Cl(1)–P(1) 2.0907(10), Cl(2)–P(1)
2.0778(11), P(1)–N(1) 1.6588(17), N(1)–C(1) 1.417(2), C(1)–C(1)0 1.323(4),
N(1)–P(1)–Cl(2) 101.41(7), N(1)–P(1)–Cl(1) 103.17(7), Cl(2)–P(1)–Cl(1)
To a suspension of ‘‘GaI’’ (14.3 mmol) in toluene
(80 cm3) at ꢀ78 °C was added a solution of {N(Ar)C(Me)}2
(2.90 g, 7.2 mmol) in toluene (20 cm3). The resultant sus-
pension was warmed to 20 °C and stirred for 48 h to yield
a dark brown solution. Volatiles were removed in vacuo
and the residue extracted with THF (50 cm3). The extract
was filtered and the filtrate placed at ꢀ30 °C overnight to
yield 2 as orange-brown crystals (2.25 g, 43%), m.p. 195–
197 °C, IR (Nujol) m/cmꢀ1: 1627(m), 1464(m), 1377(s),
1358(s); MS APCI m/z (%): 727 [M+, 11], 599 [M+-I,
100], 474 [M+-2I, 10], MS accurate mass (EI) calc. for
C28H40N2I2Ga: m/z 727.0531, measured: 727.0529.
0
96.27(5), C(1)–N(1)–P(1) 126.56(13). Symmetry operation: ꢀx + 1, ꢀy,
˚
ꢀz. Selected bond lengths (A) and angles (°) for 10: As(1)–N(1) 1.809(4),
As(1)–Cl(1) 2.2056(15), As(1)–Cl(2) 2.2100(14), N(1)–C(1) 1.411(6), C(1)–
C(1)0 1.353(9), N(1)–As(1)–Cl(1) 98.43(13), N(1)–As(1)–Cl(2) 100.34(12),
0
Cl(1)–As(1)–Cl(2) 95.06(6). Symmetry operation:
ꢀz + 1.
ꢀx + 1, ꢀy + 2,
ECl2 fragments. The sum of the angles about P(1) in 9 is
300.9°, reflecting a compressed pyramidal geometry. In
contrast, the sum of the angles about As(1) in 10 is
293.8°, in line with the greater p-character to the E–Cl
bonds that would be expected for this compound. The E–
Cl and E–N bonds are in the normal range for both com-
pounds,1 and their Ar-DAB backbones appear to be
localized.
4.2. [I2Ga{[N(R)C(Me)]2}] (R =C6H3(C6H4 But-4)2-
2,6) (3)
To a suspension of ‘‘GaI’’ (2.85 mmol) in toluene
(80 cm3) at ꢀ78 °C was added a solution of {N(R)C(Me)}2
(0.218 g, 0.28 mmol) in toluene (20 cm3). The resultant sus-
pension was warmed to 20 °C and stirred for 48 h to yield a
dark brown solution. Volatiles were removed in vacuo and
the residue extracted with diethyl ether (10 cm3). The
extract was filtered and the filtrate placed at ꢀ30 °C over-
night to yield 3 as red crystals (0.11 g, 36%), m.p. 215–
218 °C, IR (Nujol) m/cmꢀ1: 1624(m), 1465(m), 1377(s),
1361(s); MS EI m/z (%): 1088 [M+, 4], 961 [M+-I, 100];
Anal. Calc. for C56H64N2GaI2: C, 61.78; H, 5.93; N, 2.57.
Found: C, 61.08; H, 5.78; N, 2.49%.
3. Conclusion
In summary, we have prepared several new gallium(I),
(II) and (III) heterocycles, three of which have been struc-
turally characterized. In addition, germanium(II) and (IV)
heterocycles have been prepared and fully spectroscopi-
cally characterized. Attempts to prepare N-heterocyclic
silylene, phosphenium and arsenium compounds were
unsuccessful and led to examples of silyl, phosphino and
arsino-substituted ene-amines respectively. Investigations
are underway in our laboratory into the coordination
chemistry of the gallium and germanium NHC analogues,
4 and 8. The results of this study will appear in due
course.
4.3. [K(tmeda)][:Ga{[N(Ar)C(Me)]2}] (4)
A solution of [I2Ga{[N(Ar)C(Me)]2}] (1.65 g, 2.27 mmol)
in THF (110 cm3) was added to a potassium mirror at
ꢀ78 °C with stirring. The mixture was left to stir for 120 h,
filtered and volatiles removed from the filtrate in vacuo.
TMEDA (5 cm3) and diethyl ether (10 cm3) were added to
the residue and the mixture stirred for 1 h. Volatiles were
removed in vacuo and the residue extracted into hexane
4. Experimental
All manipulations were carried out using standard
Schlenk and glove box techniques under an atmosphere
of high purity argon. THF, hexane and toluene were dis-
tilled over potassium, whilst diethyl ether was distilled over

R.J. Baker et al. / Inorganica Chimica Acta 361 (2008) 427–435
433
(40 cm3). The extract was placed at ꢀ30 °C overnight to give
MS (EI) calc. mass for C26H36Cl6N2Si2: 642.0543 measured
mass: 642.0538.
1
4 as an orange solid (0.76 g, 54%), m.p. 144–150 °C. H
3
NMR (400 MHz, C6D6,): d 1.33 (d, JHH = 6.8 Hz, 12H,
CH(CH3)2), 1.38 (d, 3JHH = 6.8 Hz, 12H, CH(CH3)2), 1.98
(s, 12H, NCH3), 2.11 (s, 6H, CH3), 2.15 (s, 4H, NCH2),
4.6. [Cl2Ge{[N(Ar)C(H)]2}] (7)
3
3.87 (sept, JHH = 6.8 Hz, 4H, CH(CH3)2), 7.15 (t,
{N(Ar)C(H)}2 (376 mg, 1.0 mmol) was dissolved in tol-
uene (20 cm3) and added to a suspension of GeCl2 Æ 1,4-
dioxane (232 mg, 1.0 mmol) in toluene (20 cm3) at
ꢀ78 °C. The resultant suspension was warmed to room
temperature and stirred for 16 h. Volatiles were then
removed in vacuo and the residue extracted into hexane
(10 cm3), and the extract placed at ꢀ30 °C to give 7 as
red-orange crystals (280 mg, 54%), m.p. 123–125 °C. 1H
NMR (300.5 MHz, C6D6, 298 K) d 1.25 (d, 3JHH = 6.9 Hz,
12H, CH(CH3)2), 1.28 (d, 3JHH = 6.9 Hz, 12H, CH(CH3)2),
3JHH = 6.8 Hz, 2H, p-ArC), 7.24 (d, 3JHH = 6.8 Hz, 4H, m-
ArC); 13C{1H} NMR (C6D6, 300 MHz) d 15.7 (CH3), 23.4
(CHCH3), 26.8 (CHCH3), 27.3 (CH), 45.3 (NCH3), 57.4
(NCH2), 121.1 (CN), 122.5 (m-ArC), 123.0 (p-ArC), 146.4
(o-ArC), 148.8 (ipso-ArC); IR (Nujol) m/cmꢀ1: 1586(s),
1558(m), 1260(s), 1096(s), 933(m); MS EI m/z (%): 405
[{N(Ar)C(Me)}2H+, 100].
4.4. [Ga{[N(Ar)C(Me)]2}]2 (5)
3
3.58 (sept, JHH = 6.9 Hz, 4H, CH(CH3)2), 5.85 (s, 2H,
To
a
solution of [K(tmeda)][:Ga{[N(Ar)C(Me)]2}]
NCH), 7.08–7.19 (m, 6H, ArH); 13C{1H} NMR
(0.34 g, 0.56 mmol) in THF (20 cm3) at 20 °C was added
Tl2SO4 (0.28 g, 0.55 mmol). The mixture was left to stir
for 120 h yielding a purple/red solution. Volatiles were
removed in vacuo and the residue extracted into diethyl
ether (40 cm3), filtered, and the filtrate concentrated and
placed at ꢀ30 °C to yield deep red crystals of 5 overnight
(0.09 g, 34%), m.p. 123 – 126 °C. 1H NMR (400 MHz,
(75.6 MHz, C6D6, 298 K) d 23.8 (CH(CH3)2), 25.6
(CH(CH3)2), 28.4 (CH(CH3)2), 124.2 (NCH), 126.9 (m-
ArC), 128.7 (p-ArC), 136.7 (o-ArC), 148.1 (ipso-ArC); IR
(Nujol) m cmꢀ1: 1611(w), 1576(w), 1382(s), 1256(s),
1212(m), 1196(s), 1180(m), 1107(s), 1054(s); MS EI m/z
(%): 521 [MH+, 10], 378 [MH+-GeCl2, 60]; Accurate mass
MS (EI) calc. mass for C26H3635Cl274GeN2: 520.1462 mea-
sured mass: 520.1458.
3
C6D6): d 1.19 (d, JHH = 6.8 Hz, 24H, CHCH3), 1.30 (d,
3JHH = 6.8 Hz, 24H, CHCH3), 1.75 (s, 12H, CH3), 3.27
3
(sept, JHH = 6.8 Hz, 8H, CHCH3), 7.18–7.26 (m, 12H,
4.7. [:Ge{[N(Ar)C(H)]2}] (8)
arom.); 13C{1H} NMR (C6D6, 300 MHz) d 14.4 (CH3),
23.0 (CHCH3), 25.4 (CHCH3), 28.0 (CHCH3), 123.1 (m-
ArC), 126.2 (p-ArC), 135.0 (o-ArC), 142.6 (ipso-ArC),
{N(Ar)C(H)}2 (376 mg, 1 mmol) was dissolved in THF
(20 cm3) and lithium powder (70 mg, 10 mmol) and a sliver
(ꢁ5 mg) of sodium added. The resultant suspension was
placed in an ultrasonic bath for three hours to give an
orange/red suspension. This was filtered and the filtrate
added to a solution of GeCl2 Æ 1,4-dioxane (232 mg,
1.0 mmol) in THF (20 cm3) at ꢀ78 °C over 5 min. The
resultant solution was warmed to room temperature and
stirred for 16 h. Volatiles were then removed in vacuo
and the residue extracted into hexane (10 cm3), and the
extract placed at ꢀ30 °C to give orange crystals of 8 over-
night (290 mg, 65%), m.p. 119–124 °C (decomp.). 1H NMR
145.4 (CN); IR (Nujol) m/cmꢀ1
: 1652(m), 1459(m),
1376(s); MS EI m/z (%): 474 [M/2+, 6], 405 [{N(Ar)C-
(Me)}2H+, 100].
4.5. [(Cl3Si)2{l-[N(Ar)C(H)]2}] (6)
{N(Ar)C(H)}2 (376 mg, 1.0 mmol) was dissolved in
THF (20 cm3) and lithium powder (70 mg, 10 mmol) and
a sliver (ꢁ5 mg) of sodium added. The resultant suspension
was placed in an ultrasonic bath for 3 h to give an orange/
red suspension. This was filtered and the filtrate cooled to
ꢀ78 °C. To the cooled solution was added silicon tetra-
chloride (0.23 cm3, 2 mmol) over 5 min. The resultant solu-
tion was warmed to room temperature and stirred for 16 h.
Volatiles were removed in vacuo and the residue extracted
into hexane (10 cm3) and the extract placed at ꢀ30 °C over-
night to give orange crystals of 6 (0.41 g, 64%), m.p. 148–
149 °C. 1H NMR (400 MHz, C6D6, 298 K) d 1.11 (d,
3
(300.5 MHz, C6D6, 298 K) d 1.20 (d, JHH = 7.0 Hz, 12H,
3
CH(CH3)2), 1.23 (d, JHH = 7.0 Hz, 12H, CH(CH3)2),
3
3.24 (sept, JHH = 7.0 Hz, 4H, CH(CH3)2), 6.73 (s, 2H,
NCH), 7.12–7.25 (m, 6H, ArH); 13C{1H} NMR
(75.6 MHz, C6D6, 298 K)
d 24.3 (CH(CH3)2), 25.6
(CH(CH3)2), 28.3 (CH(CH3)2), 123.3 (NCH), 126.4 (m-
ArC), 127.2 (p-ArC), 141.3 (o-ArC), 145.1 (ipso-ArC); IR
(Nujol) m cmꢀ1: 1669(m), 1546(m), 1323(s), 1256(s),
1185(m), 1058(m), 1043(m), 972(w); MS EI m/z (%): 450
[MH+, 11], 378 [MH+-Ge, 100]; Anal. Calc. for
C26H36N2Ge: C, 69.52; H, 8.08; N, 6.24. Found: C,
68.99; H, 7.96; H, 6.04%.
3
3JHH = 6.9 Hz, 12H, CH(CH3)2), 1.18 (d, JHH = 6.9 Hz,
12H, CH(CH3)2), 3.60 (sept, 3JHH = 6.9 Hz, 4H,
CH(CH3)2), 5.65 (s, 2H, NCH), 7.05–7.24 (m, 6H, ArH);
13C{1H} NMR (75.6 MHz, C6D6, 298 K)
d
23.7
(CH(CH3)2), 24.8 (CH(CH3)2), 28.4 (CH(CH3)2), 124.3
(NCH), 124.9 (m-ArC), 126.3 (p-ArC), 136.6 (o-ArC),
148.2 (ipso-ArC); IR (Nujol) m cmꢀ1: 1620(m), 1602(w),
1518(m), 1386(w), 1097(s), 1020(s); MS EI m/z (%): 643
[MH+, 42], 378 [{N(Ar)C(H)}2H+, 100]; accurate mass
4.8. [(Cl2P)2{l-[N(Ar)C(H)]2}] (9)
{N(Ar)C(H)}2 (376 mg, 1.0 mmol) was dissolved in
THF (20 cm3) and lithium powder (70 mg, 10 mmol) and

434
R.J. Baker et al. / Inorganica Chimica Acta 361 (2008) 427–435
a sliver (ꢁ5 mg) of sodium added. The resultant suspension
was then placed in an ultrasonic bath for 3 h to give a red-
orange suspension. This was then filtered and the filtrate
cooled to ꢀ78 °C. To the solution was added PCl3
(175 ll, 2 mmol) over 5 min. The resultant solution was
warmed to room temperature and stirred for 16 h. Volatiles
were removed in vacuo and the residue extracted into hex-
ane (10 cm3). The extract was placed at ꢀ30 °C overnight
to give red-orange crystals of 9 (325 mg, 56%), m.p. 122–
(SHELX97) [22] using all unique data. Crystal data, details of
data collections and refinement are given in Table 1.
Acknowledgements
We gratefully acknowledge financial support from the
EPSRC (postdoctoral fellowships for R.J.B. and M.W.,
studentship for D.P.M.). We also thank the EPSRC Mass
Spectrometry Service and the Australian Research Council
(fellowship for CJ).
1
125 °C (decomp.). H NMR (300.5 MHz, C6D6, 298 K) d
3
1.17 (d, JHH = 6.7 Hz, 12H, CH(CH3)2), 1.20 (d,
3JHH = 6.7 Hz,
12H,
CH(CH3)2),
3.17
(sept,
Appendix A. Supplementary material
3JHH = 6.7 Hz, 4H, CH(CH3)2), 6.11 (s, 2H, NCH), 7.05–
7.19 (m, 6H, ArH); 13C{1H} NMR (75.6 MHz, C6D6,
CCDC 626093, 626094, 626095, 626096, 626097 and
626098 contain the supplementary crystallographic data
for 2, 3 Æ (diethyl ether)0.50, 5 Æ (diethyl ether)0.33, 7, 9 and
10. These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or
e-mail: deposit@ccdc.cam.ac.uk. Supplementary data asso-
ciated with this article can be found, in the online version,
at doi:10.1016/j.ica.2006.12.014.
298 K)
d 24.6 (CH(CH3)2), 25.1 (CH(CH3)2), 28.8
2
(CH(CH3)2), 120.8 (d, JPC = 8.1 Hz, NCH), 124.6 (m-
ArC), 125.0 (p-ArC), 134.0 (o-ArC), 148.8 (d,
2JPC = 4.6 Hz, ipso-ArC); IR (Nujol) m cmꢀ1: 1634(w),
1588(w), 1378(s), 1261(s), 1192(m), 1107(m), 1056(m),
1042(m); MS APCI m/z (%): 579 [M+, 11], 378 [MH+-
2PCl2, 100]; Accurate mass MS (EI) calc. mass for
C26H36Cl4N2P2: 578.1102 measured mass: 578.1104.
4.9. [(Cl2As)2{l-[N(Ar)C(H)]2}] (10)
References
{N(Ar)C(H)}2 (376 mg, 1.0 mmol) was dissolved in
THF (20 cm3) and lithium powder (70 mg, 10 mmol) and
a sliver (ꢁ5 mg) of sodium added. The resultant suspension
was then placed in an ultrasonic bath for 3 h to give a red-
orange suspension. This was then filtered and the filtrate
cooled to ꢀ78 °C. To the solution was added AsCl3
(2 mmol) over 5 min. The resultant solution was warmed
to room temperature and stirred for 16 h. Volatiles were
removed in vacuo and the residue extracted into hexane
(10 cm3). The extract was placed at ꢀ30 °C overnight to
give red-orange crystals of 10 (320 mg, 48%), m.p. 104–
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